Controlled removal of off-gas from oxygen steel converters

ABSTRACT

A plurality of oxygen steel converters discharge off-gas streams via individual air-ventilated hoods to a common disposal system. The dampers which control individual hood off-gas flows are modulated to provide an adequate removal rate from a converter hood at the peak of the blow period.

United States Patent Brown et a].

[15] 3,655,361 [4 1 Apr. 11, 1972 [54] CONTROLLED REMOVAL OF OFF-GAS FROM OXYGEN STEEL CONVERTERS [72] Inventors: Bernard C. Brown, East Rockaway, N.Y.;

Frank C. Braemer, Teaneck, NJ.

[73] Assignee: Chemical Construction Corporation, New

York, N.Y.

[22] Filed: Nov. 20, 1969 [2!] Appl. No.: 878,435

[52] U.S. Cl ..75/60, 122/7, 266/15, 266/31, 266/35 [51] Int. Cl ..C2lc 5/38 [58] Field of Search ..75/59, 60; 266/31, 35,15; 122/7 A [56] References Cited UNITED STATES PATENTS 3,357,820 12/1967 Rasworscheggetal ..266/35X 3,416,470 12/1968 Hey et a1 ..122/7 2,831,467 4/1958 Guczky ..122/7 3,143,411 8/1964 Hoff ..75/60X 3,480,427 11/1969 Denig et al ..266/15 X 3,063,694 Il/l962 Gaw ..266/15 3 ,224,84 I I 2/ I 965 Kemmetmuller ..266/ 3 1 FOREIGN PATENTS OR APPLICATIONS 294,565 I/1967 Australia ..75/60 1,072,356 6/ I 967 Great Britain ..75/60 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. White A tt0rney-J. L. Chaboty [57] ABSTRACT A plurality of oxygen steel converters discharge off-gas streams via individual air-ventilated hoods to a common disposal system. The dampers which control individual hood off-gas flows are modulated to provide an adequate removal rate from a converter hood at the peak of the blow period.

3 Claims, 1 Drawing Figure PATENTEDAPR 11 I972 BERNARD C. BROWN FRANK C. BRAEMER JR.

W Va ITORS,

AGENT CONTROLLED REMOVAL OF OFF-GAS FROM OXYGEN STEEL CONVERTERS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the operation of oxygen steel converters in which a gaseous stream of substantially pure oxygen is blown into the converter to react with the carbon content of a ferrous metal melt in the converter, and thereby generate an off-gas rich in carbon monoxide, which is removed via an airventilated hood.

2. Description of the Prior Art The general prior art practice is to operate a plurality of converters discharging off-gas to a common disposal system with a constant total gas volume, as shown in U.S. Pat. No. 3,409,283. This system does not adequately accommodate for operation with alternate peaking of the blow period, since the colder vessel has a greater proportion of off-gas extracted through its hood than is required into the common disposal system, and the hotter vessel does not receive adequate ventilation, with resultant discharge of off-gas about the periphery of the converter mouth, hood and oxygen lance opening. Other converter systems are shown in British Pat. No. 1,072,356, U.S. Pat. Nos. 3,416,470; 3,194,651; 3,177,065; 3,154,406; 3,111,400; 2,803,450 and German Pat. No. 1,019,336.

SUMMARY OF THE INVENTION In the present invention, a first and a second converter discharge off-gas streams into their respective air-ventilated hoods, which are connected to a common disposal system. The carbon monoxide content of the off-gases reacts with the oxygen content of the inducted excess air in each hood to form carbon dioxide. A resultant first off-gas stream is drawn from the air ventilated hood of the first converter to the common disposal system at a rate which is regulated to provide excess inducted air, so that an excess oxygen proportion is maintained in the first off-gas stream. The first converter generates carbon monoxide at a high volumetric flow rate, typically at the peak of the blow period, and the first off-gas is formed at a highly elevated temperature. The second converter generates carbon monoxide at a low volumetric flow rate which is less than the volumetric flow rate of carbon monoxide from the first converter, and the second off-gas stream is formed at a lower elevated temperature than the first off-gas stream. The second off-gas stream is passed from the air-ventilated hood of the second converter to the common disposal system at a rate which is purposely restricted by a throttling damper or the like, so that a greater volumetric flow rate of otY-gas is removed from the hood of the first converter than from the hood of the second converter.

The principal advantage of the invention is that the available volumetric gas handling capacity of the common disposal system is properly divided between the two operating converter vessels in relation to their requirements. Another advantage is that adequate ventilation is provided for the converter operating at the peak of the blow period. A further advantage is that discharge of off-gas into the surrounding shop atmosphere from about the mouth of the converter, lower periphery of the hood or oxygen lance opening is prevented during all phases of the operating cycle. Another important advantage in this temperature or oxygen control system is the reduction of the gas volume from the blowing vessel or vessels during the off-peak periods when less carbon monoxide is generated and therefore less air is required to burn this carbon monoxide to carbon dioxide. This will reduce the scrubber system fan horsepower requirements, or make the extra capacity of the scrubber system available during overlapping blows to increase the oxygen blowing rate.

It is an object of the present invention to provide an improved method of operating a plurality of oxygen steel converters which discharge off-gas streams to a common disposal system.

Another object is to provide adequate air ventilation for the hood of an oxygen steel converter during the peak of the blow period, when the hood discharges ofi-gas to a disposal system which is common to a plurality of converters.

A further object is to properly divide the available gas handling capacity of a common disposal system which simultaneously receives off-gas from the air-ventilated hoods of a plurality of oxygen steel converters.

An additional object is to prevent the discharge of digits into the surrounding shop atmosphere from the air ventilated hood of an oxygen steel converter.

These and other objects and advantages of the present invention will become evident from the description which follows.

DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENTS Referring now to the drawing, a flowsheet showing several alternative embodiments and control sequences of the invention is presented. Oxygen steel converter 1 is provided with a pool or charge 2 consisting of molten ferrous metal containing impurities including carbon. A gas stream 3 consisting of substantially pure oxygen is passed via oxygen lance 4 into converter l, which is at the peak of the blow period with con sequent maximum flow rate of oxygen input via stream 3. The injected oxygen reacts with the carbon content of charge 2 to form a gas stream 5 principally containing carbon monoxide which is discharged upwards from the mouth 6 of the converter l. Stream 5 mixes and reacts with air stream 7, which is inducted upwards into the air-ventilated hood 8 around the outer periphery of mouth 6. A portion of the oxygen content of stream 7 reacts with the carbon monoxide derived from stream 5 to form a very hot gas stream 9 within the gas conduit 10 which extends upwards from hood 8. Inclined conduit section 11 extends upwards from conduit 10 to vertical gas rise conduit 12, which passes the gas stream into the downwardly extending gas quench conduit 13.

A liquid quench stream 14 generally consisting of water passes via pipe 15 into conduit 13, and is sprayed downwards into the hot gas stream via spray nozzle 16. An inverted frustoconical baffle 17 extends downwards within conduit 13 below nozzle 16, and accelerates the gas stream to high velocity to insure uniform gas-liquid mixing. The quenched gas stream next flows from vertical conduit 13 into the horizontal conduit 18 in which regulation of off-gas flow rate is attained by adjustment or modulation of damper 19. A controller 20 adjusts damper 19 to a desired setting, which in this instance is a maximum gas flow position, since converter 1 is at the peak of the blow period, as mentioned supra. A gas stream variable sampling element 21 extends to sensor or measuring device 22, which in turn transmits a signal to controller 20 via linkage or transfer means 23.

Element 21 may measure one of several process variables in the quenched gas stream within conduit 18. The regulated rate of flow of the off-gas stream within conduit 18 may be maintained by measuring the oxygen content of the off-gas stream via elements 21 and 22, and adjusting the flow rate of the offgas by modulating damper 19 in an inverse proportion to oxygen content, so that a substantially constant free oxygen content is maintained in the off-gas stream. In other instances, the temperature of the quenched olT-gas may be measured by element 21, with resultant modulation of damper 19 in a direct proportion to quenched off-gas temperature, so that a substantially constant quenched off-gas temperature is maintained.

A second oxygen steel converter 24 is provided in the shop, together with converter 1. The considerations described supra with respect to converter 1 also apply to converter 24, except that converter 24 is operating at an interval of the blow period other than the peak of the blow, and therefore the operation of converter 24 will only be briefly described. Pool or charge 25 consisting of molten ferrous metal is disposed in converter 24, and oxygen stream 26 is passed through lance 27. Unit 24 is at either the beginning or terminal portion of the blow period. The resulting generated carbon monoxide-rich off-gas stream 28 is produced at a low rate compared to stream 5, and flows upwards through the mouth 29 of unit 24 for mixing and reaction with the air stream 30 which flows into the air-ventilated hood 31. The resulting gas stream 32 flows upwards through vertical conduit 33, inclined conduit 34 and vertical conduit 35, and downwards through vertical gas quench conduit 36. Quench water stream 37 is injected into the hot gas stream via pipe 38 and spray nozzle 39, with equilibrium being attained by the provision of inverted frusto-conical baffle 40 within conduit 36 below nozzle 39.

The resulting quenched gas stream flows from conduit 36 into horizontal conduit 41 which is provided with an internal gas flow modulating damper 42, which in this embodiment of the invention is adjusted to restrict gas flow rate to a magnitude less than the gas stream flow rate through conduit 18. Controller 43 adjusts damper 42 to an inclined position, so as to restrict or throttle off-gas flow through conduit 41. A control variable of the gas in conduit 41, such as oxygen content or temperature, is sensed by element 44 and measured by measuring and regulating device 45, which adjusts controller 43 via transmission line 46.

Since the invention is generally applicable to a plurality of oxygen steel converters discharging off-gas to a common disposal system, a conduit 47 is shown which transmits a quenched off-gas stream 48 to the junction between conduits l8 and 41 from a third oxygen steel converter, not shown, and its appurtenances including an air-ventilated hood, quencher and modulating damper.

The quenched off-gas flows as a combined stream from the junction of conduits 18, 41 and 47 into a common disposal system which is provided downstream of the gas removal conduit 49. The combined gas stream flows downwards through conduit 49 and into the venturi gas scrubber defined by approach section 50, throat 1 and pressure recovery section 52, in which the gas stream is scrubbed to remove entrained solid particles such as iron oxide fume. Scrubbing liquid streams 53 are passed via pipes 54 transversely into the highly accelerated gas stream at the throat section 51 and the gas stream is effectively and uniformly scrubbed free of solid particles. The resultant mixture of scrubbed gas and liquid droplets flows downwards from section 52 through the depending conduit 55, which transfers the gas-liquid droplets mixture to the gasliquid separator 56. The separator unit 56 is generally a cyclonic or baffled vessel which separates the entrained liquid droplets phase from the scrubbed gas stream. The separated liquid phase containing separated solids is removed from unit 56 as liquid or slurry stream 57. The scrubbed gas is removed from unit 56 via conduit 58, which transfers the gas to induction blower 59, which discharges the gas to disposal via conduit 60 as stream 61.

At the beginning of the blow, no carbon monoxide is formed. The oxygen controller will tend to fully close the damper in the furnace exit, if the system is operated on oxygen control. Therefore, a minimum closed position is provided for damper 42, which permits some gaseous flow even when no off-gas is generated. The system may also be operated based on constant standard cubic feet per minute (SCFM) of gas flow, in which, regardless of actual cubic feet per minute (ACFM) generated by the converters, the gas flow is measured in terms of equivalent SCFM and the dampers are adjusted to provide constant SCFM of gas flow from each converter.

An example of an industrial application of the present invention will now be described.

EXAMPLE A system was designed for a two-converter shop, in which both units discharged to a common gas cleaning and cooling system. The gas cleaningsystem was sized adequately to handie twice the volume required for one converter at the peak of the blow. The required volume for each converter at the peak of the blow was l63,000 SCFM, based on 20,000 SCFM oxygen blow and 50 percent excess air ratio. Under these design conditions, with both converters peaking simultaneously, the total gas volume discharged through the cleaning and cooling system was a constant value of two times 163,000 SCFM or 326,000 SCFM.

The approximate actual distribution of off-gas flows was determined, for a condition in which the fust converter was at the peak of the blow, with high carbon monoxide evolution rate, and the second converter was at the end of the blow, with low carbon monoxide evolution rate, and with both converters discharging oif-gas to the common disposal system which had a constant total gas handling capacity of 326,000 SCFM. The actual distribution of off-gas flows without the control sequence and damper modulation of the present invention was about 1,080,000 ACFM or 135,000 SCFM from the first converter, which resulted in a deficiency of off-gas removal; and about 764,000 ACFM or 191,000 SCFM from the second converter, which resulted in excessive off-gas removal from the second and colder vessel at the end of the blow.

Under the conditions and applying damper modulation in accordance with the present invention, the first converter had an off-gas flow at 1,950 C. of about 600,000 ACFM or 163,000 SCFM, and the second converter had an ofi gas flow at 800 C. of about 300,000 ACFM or 163,000 SCFM, which was the same SCFM of gas flow as the first converter, and the desired equalization of off-gas flows was attained.

Without application of the method of the present invention, equal distribution is destroyed through effects of gas temperatures in an everchanging relationship as the blows proceed. The situation becomes worse when the total scrubber or gas cleaning capacity is less than that required for two vessels peaking simultaneously.

We claim:

1. A method of operating a plurality of oxygen steel converters which discharge off-gas streams to a common disposal system which comprises passing a first off-gas stream from the air-ventilated hood of a first converter to said common disposal system at a regulated rate whereby a substantially constant excess oxygen proportion is maintained in said first off-gas stream, said regulated rate of flow of said first off-gas stream being maintained by measuring the oxygen content in said first off-gas stream, and adjusting the flow rate of said first off-gas stream in an inverse proportion to oxygen content, whereby said substantially constant free oxygen content is maintained in said first off-gas stream, said first converter generating carbon monoxide at a high volumetric flow rate whereby said first off-gas stream is formed at a highly elevated temperature, and passing a second off-gas stream from the airventilated hood of a second converter to said common disposal system at a restricted rate, whereby a greater volumetric flow rate of off-gas is removed from the hood of said first converter than from the hood of said second converter, said second converter generating carbon monoxide at a low volumetric flow rate which is less than the volumetric flow rate of carbon monoxide from said first converter, whereby said second off-gas stream is formed at a lower elevated temperature than said first off-gas stream.

2. A method of operating a plurality of oxygen steel converters which discharge off-gas streams to a common disposal system which comprises passing a first off-gas stream from the air-ventilated hood of a first converter to said common disposal system at a regulated rate whereby a substantially constant excess oxygen proportion is maintained in said first off-gas stream, said regulated rate of flow of said first off-gas stream being maintained by measuring the oxygen content in said first off-gas stream, and adjusting the flow rate of said first off-gas stream in an inverse proportion to oxygen content, whereby said substantially constant free oxygen content is maintained in said first ofi-gas stream, said first converter generating carbon monoxide at a high volumetric flow rate whereby said first off-gas stream is formed at a highly elevated temperature, and passing a second off-gas stream from the airventilated hood of a second converter to said common disposal system at a restricted rate less than the regulated fiow rate of said first off-gas stream, whereby a substantially constant total volumetric flow rate of combined dry off-gas streams to said common disposal system is maintained, said second converter generating carbon monoxide at a low volumetric fiow rate which is less than the volumetric flow rate of carbon monoxide from said first converter, whereby said second off-gas stream is formed at a lower elevated temperature than said first off-gas stream.

3. A method of operating a plurality of oxygen steel converters which discharge off-gas streams to a common disposal system which comprises passing a first off-gas stream from the air-ventilated hood of a first converter to said common disposal system at a regulated rate whereby an excess oxygen proportion is maintained in said first off-gas stream, said first off-gas stream being saturated to a reduced temperature by direct contact with water prior to passing into said common disposal system, said regulated rate of flow of said first off-gas stream being maintained by measuring the temperature of the saturated off-gas, and adjusting the flow rate of said first offgas stream in a direct proportion to saturated off-gas temperature, whereby a substantially constant saturated off-gas temperature is maintained, said first converter generating carbon monoxide at a high volumetric flow rate whereby said first 01?- gas stream is formed at a highly elevated temperature, and passing a second off-gas stream from the air-ventilated hood of a second converter to said common disposal system at a restricted rate less than the regulated flow rate of said first oligas stream, whereby a substantially constant total volumetric flow rate of combined dry off-gas streams to said common disposal system is maintained, said second converter generating carbon monoxide at a low volumetric flow rate which is less than the volumetric flow rate of carbon monoxide from said first converter, whereby said second off-gas stream is formed at a lower elevated temperature than said first off-gas stream. 

2. A method of operating a plurality of oxygen steel converters which discharge off-gas streams to a common disposal system which comprises passing a first off-gas stream from the air-ventilated hood of a first converter to said common disposal system at a regulated rate whereby a substantially constant excess oxygen proportion is maintained in said first off-gas stream, said regulated rate of flow of said first off-gas stream being maintained by measuring the oxygen content in said first off-gas stream, and adjusting the flow rate of said first off-gas stream in an inverse proportion to oxygen content, whereby said substantially constant free oxygen content is maintained in said first off-gas stream, said first converter generating carbon monoxide at a high volumetric flow rate whereby said first off-gas stream is formed at a highly elevated temperature, and passing a second off-gas stream from the air-ventilated hood of a second converter to said common disposal system at a restricted rate less than the regulated flow rate of said first off-gas stream, whereby a substantially constant total volumetric flow rate of combined dry off-gas streams to said common disposal system is maintained, said second converter generating carbon monoxide at a low volumetric flow rate which is less than the volumetric flow rate of carbon monoxide from said first converter, whereby said second off-gas stream is formed at a lower elevated temperature than said first off-gas stream.
 3. A method of operating a plurality of oxygen steel converters which discharge off-gas streams to a common disposal system which comprises passing a first off-gas stream from the air-ventilated hood of a first converter to said common disposal system at a regulated rate whereby an excess oxygen proportion is maintained in said first off-gas stream, said first off-gas stream being saturated to a reduced temperature by direct contact with water prior to passing into said common disposal system, said regulated rate of flow of said first off-gas stream being maintained by measuring the temperature of the saturated off-gas, and adjusting the flow rate of said first off-gas stream in a direct proportion to saturated off-gas temperature, whereby a substantially constant saturated off-gas temperature is maintained, said first converter generating carbon monoxide at a high volumetric flow rate whereby said first off-gas stream is formed at a highly elevated temperature, and passing a second off-gas stream from the air-ventilated hood of a second converter to said common disposal system at a restricted rate less than the regulated flow rate of said first off-gas stream, whereby a substantially constant total volumetric flow rate of combined dry off-gas streams to said common disposal system is maintained, said second converter generating carbon monoxide at a low volumetric flow rate which is less than the volumetric flow rate of carbon monoxide from said first converter, whereby said second off-gas stream is formed at a lower elevated temperature than said first off-gas stream. 